Process for preparing 1,6-hexanediol

ABSTRACT

The invention provides 1,6-hexanediol having a proportion by weight of nitrogen of less than 5 ppm, and polymers obtained by reacting the 1,6-hexanediol with at least one reactive compound. The 1,6-hexanediol is obtained by distilling a mixture including 1,6-hexanediol and more than 500 ppm of at least one carboxylic acid, ester, or both, having a boiling point higher than that of the 1,6-hexanediol and being in contact with the 1,6-hexanediol at a temperature range greater than or equal to 100° C. for at least 5 minutes before, during, or before and during, the distillation, followed by collection of the 1,6-hexanediol. In certain embodiments of this invention, the 1,6-hexanediol has a proportion by weight of nitrogen of less than 3 ppm and less than 2 ppm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/952,956 filed Nov. 23, 2010 and claims priority of German patentapplication No. 10 2009 047 196.0 filed Nov. 26, 2009.

BACKGROUND OF THE INVENTION

The invention relates to a process for preparing 1,6-hexanediol, inwhich a hexanediol having a proportion by weight of nitrogen of lessthan 5 ppm is obtained, 1,6-hexane-diol having a proportion by weight ofnitrogen of less than 5 ppm and also the use of this 1,6-hexanediol forpreparing polymers.

There is a great demand for 1,6-hexanediol which has no amines inamounts which have a catalytic effect in the preparation ofpolyurethanes, since these catalytic amounts of amines lead toconsiderable amounts of by-products which hinder the reaction to formthe polyurethane.

DE 10112117 A1 describes a process for removing nitrogen-comprisingcompounds using acidic and/or basic ion exchangers. The proportion byweight of nitrogen is determined here by means of a CPR (controlledpolymerization rate). This purification process has the disadvantagethat the use of acidic and/or basic ion exchangers leads to increasedcosts since the ion exchangers themselves represent costs and their usemeans an increased use of solvents since ion exchangers are onlyfinitely useable and have to be regenerated every now and again. Inaddition, to avoid losses of product, rinsing of the ion exchanger isnecessary and leads to increased use of solvents or regeneration media.Since 1,6-hexanediol is solid under normal conditions, the feed to theion exchanger has to be additionally heated for a reaction over the ionexchanger to be possible at all. Thus, the process for purifyingpolyalcohols in DE 101112117 A1 has considerable disadvantages.Furthermore, DE 101112117 A1 does not describe the removal ofnitrogen-comprising compounds from 1,6-hexanediol.

The preparation of 1,6-hexanediol starts out from the appropriatecyclo-C₆-alkanes, alcohols, ketones and/or mixtures of these compounds,and these are either oxidized in the presence of nitric acid and/orsubjected to oxidation with subsequent water extraction of the organicstream.

In the case of 1,6-hexanediol, streams comprising adipic acid areproduced in this way from, for example, cyclohexanol and/orcyclohexanone by oxidation using nitric acid. For the present purposes,streams comprising adipic acid are streams which can comprise adipicacid itself or else adipic acid in the form of its esters. In theoxidation, it is possible to use both the adipic acid obtained byoxidation and the mixture remaining after the adipic acid has largelybeen separated off, which mixture comprises adipic acid, glutaric acidand succinic acid.

Furthermore, other sources of adipic acid or streams comprising adipicacid are in principle streams which can be mixed with the abovementionedstreams, for example streams obtained by oxidation of cyclohexane tocyclohexanol/cyclohexanone mixtures and subsequent water extraction ofthe organic stream.

The abovementioned streams usually comprise impurities which in the caseof the oxidation of cyclohexanol/cyclohexanone are formed by oxidationusing nitric acid and comprise nitrogen. Nitrogen components are alsopresent as undesirable secondary components in the water extracts afterthe oxidation of cyclohexane by means of air.

These nitrogen compounds, which can be present, for example, as nitrogroup, amides or ammonium ion, are able to form amines during thehydrogenation of streams comprising adipic acid, which can also beesterified. For example, nitro compounds can be hydrogenated directly toamines and/or amides. Ammonium ions can aminate alcohols formed duringthe hydrogenation.

Amines are basic components and as such are undesirable in1,6-hexanediol since they have properties which are undesirable in theuses of 1,6-hexanediol. Thus, these amines can, for example, have acatalytic action in the preparation of polyurethanes, so that processcontrol for preparing a product having precisely defined properties isdifficult if not impossible. It can happen that entire productionbatches have to be disposed of. This also applies in principle in thepreparation of polyesters or polyester alcohols which are then againreacted further with isocyanates to form urethanes.

One possible way of establishing whether undesirable N-comprisingcompounds are present in the form of basically acting amines in1,6-hexanediol is to determine the CPR (controlled polymerization rate).The content of basically acting amine is accordingly coupled with theCPR and can, as explained for the example of 1,6-hexanediol, bedetermined as follows:

-   -   30 g of 1,6-hexanediol are dissolved in 100 ml of a solution of        potassium hydroxide in methanol (0.001 mol/l) and stirred for 15        minutes. This solution is, for example, titrated        potentiometrically with 0.01N hydrochloric acid to the end point        using a Titroprocessor 682™ from Metrohm, Herison, Switzerland.        The Titroprocessor 682 is equipped with two pH electrodes, viz.        a glass electrode (3 M KCl, Metrohm 6.0133.100) and an        Ag/AgCl/LiCl electrode (alcohol, Metrohm 6.0726.100). The        procedure is repeated using a comparative solution comprising        100 ml of a solution of potassium hydroxide in methanol (0.001        mol/l) to determine the blank.

The CPR is determined from the two results of potentiometric titrationas follows:CPR=10×(V1−V2), where

-   -   V1 is the consumption of 0.01N hydrochloric acid in the case of        the polyalcohol sample,    -   V2 is the consumption in the comparison (blank) and    -   10 corresponds to the calculation factor in accordance with JIS        (Japan Industrial Standard) K 1557-1970.

For example, at a CPR of 10, i.e. a net hydrochloric acid consumption of1 g of 0.01 molar HCl, about 5 ppm of N is present in the1,6-hexanediol. Such a CPR of 10, i.e. an N content of 5 ppm, is alreadyan undesirably high level and can cause considerable secondary reactionsin subsequent polyurethane reactions.

It is therefore an object of the present invention to provide a processwhich makes it possible to prepare 1,6-hexanediol having a CPR of lessthan 10, without an additional outlay and costs associated withadditional solvents and/or acidic and/or basic ion exchangers having tobe incurred.

BRIEF SUMMARY OF THE INVENTION

This object is achieved by a process for purifying 1,6-hexanediol, whichcomprises the following steps

-   -   I) provision of a mixture comprising 1,6-hexanediol    -   II) distillation of this mixture from step I    -   III) collection of a 1,6-hexanediol having a nitrogen content of        less than 5 ppm,        wherein more than 500 ppm of carboxylic acids and/or esters        which have a boiling point higher than that of 1,6-hexanediol        and are in contact with the 1,6-hexanediol at temperatures of        ≧100° C. for at least 5 minutes are comprised before and/or        during the distillation in step II.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, it is necessary for the mixture fromstep I of the process of the invention which is to be distilled tocomprise not only 1,6-hexanediol but also carboxylic acids and/or esterswhich have a boiling point higher than that of 1,6-hexanediol itself.This can be achieved by the mixture used in step I) comprising not only1,6-hexanediol but also carboxylic acids and/or esters which formhigher-boiling esters with 1,6-hexanediol or else, before and/or duringthe distillation in step II, either carboxylic acids and/or estershaving a boiling point higher than that of 1,6-hexanediol (high boilers)being added to the mixture from step I or carboxylic acids and/or esterswhich react with part of the 1,6-hexanediol to form esters which afterthe reaction have a boiling point higher than that of 1,6-hexanediol areadded. It is also possible to use mixtures of high boilers andcarboxylic acids and/or esters which with 1,6-hexanediol form estershaving a boiling point higher than that of 1,6-hexanediol itself.

When high boilers or carboxylic acids and/or esters which formhigher-boiling esters with 1,6-hexanediol itself are added before and/orduring the actual distillation in step II, then the distillation has tobe carried out so that these high boilers and/or higher-boiling estersare in contact with the 1,6-hexanediol in the mixture from step I for aparticular time before the 1,6-hexanediol is distilled off. This contacttime during the distillation has to be at a temperature of ≧100° C. forat least 5 minutes. Preference is given to a contact time of ≧10minutes, particularly preferably a contact time of ≧15 minutes. For thepurposes of the present invention, the contact time is the time forwhich the 1,6-hexanediol is in contact with the high boiler and/or thehigher-boiling esters in the liquid or gaseous state within the column.The contact space in which the 1,6-hexanediol has to be in contact withthe high boiler and/or the higher-boiling esters is the entire columnand also the associated piping and, if appropriate, the vaporizer. Thecontact space thus comprises the packing within the column, thecollectors and distributors and also the associated piping, the bottomof the column and also any attached vaporizer and the pipe to this.

The temperature during the contact time should be ≧100° C., preferablyat least 120° C., particularly preferably at least 140° C.

The carboxylic acids and/or esters which are if appropriate added to themixture from step I before the distillation in step II are selected fromthe group consisting of adipic acid, adipic esters, 6-hydroxycaproicacid, 6-hydroxycaproic esters. Particular preference is given to theesters selected from the group consisting of dimethyl adipate, methyl6-hydroxycaproate, 1,6-hexanediol methyl adipate, the di-1,6-hexanediolester of adipic acid, the 1,6-hexanediol ester of 6-hydroxycaproic acidand mixtures of these esters.

The amount of carboxylic acids and/or esters which are reacted with the1,6-hexanediol to form the higher-boiling esters and also the amount ofhigh boilers added and the amount of mixtures of added high boilers andcarboxylic acids and/or esters which are reacted with 1,6-hexanediol toform the higher-boiling esters are in the range of ≧500 ppm, preferablyin the range of ≧1000 ppm, particularly preferably ≧1500 ppm, based onthe amount of 1,6-hexanediol to be distilled.

The pressures during the distillation are preferably in the range from 5to 3000 mbar absolute. Before the actual distillation in step II of theprocess of the invention, other compounds can, if appropriate, bedistilled off beforehand. These are in particular compounds which have aboiling point at least 50° C. lower than that of 1,6-hexanediol itselfand are referred to as low boilers. The low boilers are preferablyselected from the group consisting of methanol, water, dimethyl ether,1-hexanol and 1-methoxy-6-hydroxyhexane. The low boilers can beseparated off in a separate column which is located upstream of thedistillation in step II. The pressure within this column for separatingoff the low boilers is, for example when methanol and/or water are to beseparated off, in the range from 200 to 3000 mbar absolute, and when1,6-hexanediol is to be separated off from high boilers and/or thehigher-boiling esters, the pressure during this distillation is in therange from 5, preferably 10 to 500 mbar absolute, preferably in therange from 20 to 300 mbar absolute, particularly preferably in the rangefrom 30 to 200 mbar absolute.

The distillations can be carried out as batch process or continuously,but preference is given to continuous operation, especially when1,6-hexanediol is to be produced in industrial amounts.

To prepare 1,6-hexanediol having a proportion by weight of nitrogen ofless than 5 ppm, adipic acid which has been prepared either by oxidationof cyclohexanol and/or cyclohexanone by means of nitric acid, byoxidation of cyclohexane to cyclo-hexanol/cyclohexanone mixtures andsubsequent water extraction of the organic stream or by oxidation ofcyclohexane by means of air and subsequent water extraction is used asstarting material. Here, the adipic acid comprising the solutions isesterified with an alcohol selected from the group consisting ofmethanol, ethanol, propanol, isopropanol, n-butanol, isobutanol,pentanols, hexanols, 2-ethylhexanol, 2-propylheptanol, 1,5-pentanediol,1,6-hexanediol, tridecanol, pentadecanol and mixtures of the alcohols,preferably methanol, ethanol, propanol, n-butanol and 1,6-hexanediol.Particular preference is given to methanol and 1,6-hexanediol foresterification. The subsequent hydrogenation can be carried out in thegas phase or in the liquid phase.

When the subsequent hydrogenation is to be carried out in the gas phase,methanol is preferred as alcohol for esterification.

If hydrogenation is to be carried out in the liquid phase, not onlymethanol but also 1,6-hexanediol are preferred.

The alcohol is used in an at least equimolar amount relative to thecarboxyl groups of the adipic acid and, if appropriate, other carboxylgroups of other acids which may be present. However, preference is givento a molar excess of alcohol per carboxyl group of at least 2.

The esterification can proceed without added catalyst, but preference isgiven to using one catalyst after an acid conversion of 50% by weight.This can be, for example, sulfuric acid or sulfonic acids, but alsoacidic solids such as ion exchangers, usually ion exchangers based onsulfonic acid.

The water of reaction formed is preferably separated off during theesterification, e.g. by distillation. Alcohol is also entrained. Forthis reason, preference is given to distilling the alcohol/water mixtureseparately and recirculating the alcohol.

Depending on the esterification technology, the dialkyl adipate can beobtained in a form ready for use in the hydrogenation, but it can alsobe that alcohol and water still have to be separated off or the dialkyladipate has to be purified by distillation in order to separate offincompletely reacted acid which is either disposed of or preferably, ifappropriate after discharge of a small percentage to avoid accumulationof undesirable components, recirculated to the esterification. Theoptionally purified dialkyl adipate is subsequently hydrogenated.

This can occur in the liquid phase or gas phase, preferably overCu-comprising catalysts.

In the liquid-phase hydrogenation, preference is given to employingpressures of 100-330 bar absolute, preferably a gauge pressure of150-270 bar, while in the gas phase a gauge pressure of from 5 to 100bar is appropriate, with particular preference being given to from 20 to70 bar.

It is advantageous for the hydrogenation product mixture still tocomprise carboxyl groups, preferably esters. These can be, for example,dimethyl adipate, methyl 6-hydroxycaproate, 1,6-hexanediol methyladipate, the di-1,6-hexanediol ester of adipic acid and/or the1,6-hexanediol ester of 6-hydroxycaproic acid. If exclusively orvirtually exclusively dimethyl adipate and/or methyl 6-hydroxycaproateare to be present as carboxyl-comprising compounds in the hydrogenationproduct mixture, it has to be ensured in the subsequent distillationstage(s) or in a separate stage that these esters are not distilled offcompletely from 1,6-hexanediol. In the process of the invention, theseesters are reacted with 1,6-hexanediol at temperatures of ≧100° C. toform corresponding esters having a boiling point higher than1,6-hexanediol itself. These corresponding higher-boiling esters areselected from the group consisting of 1,6-hexanediol methyl adipate, thedi-1,6-hexanediol ester of adipic acid and/or the 1,6-hexanediol esterof 6-hydroxycaproic acid. The content of these higher-boiling estersbased on the content of 1,6-hexanediol is at least 500 ppm, preferably≧1000 ppm, particularly preferably ≧1500 ppm.

The reaction of dimethyl adipate and methyl 6-hydroxycaproate with1,6-hexanediol can occur either purely thermally or in the presence ofcatalytically active compounds such as acids or bases. Preference isgiven to the thermal variant in which the temperature is ≧100° C. andthe time for which the esters and 1,6-hexanediol are in contact has tobe at least 5 minutes. Preference is given to temperatures of ≧120° C.and contact times of ≧10 minutes.

In a preferred embodiment, if methyl esters have been used in thehydrogenation, at least 50% of the methanol has been removed bydistillation before this contact time. This is preferably combined withthe methanol removal step which precedes the actual distillation in stepII.

The mixture comprising 1,6-hexanediol, the high boilers, higher-boilingesters and if appropriate low boilers is fractionally distilled. Here,compounds having a boiling point lower than that of 1,6-hexanediol, forexample the low boilers such as methanol, are preferably separated offby distillation in a first distillation unit, e.g. a continuouslyoperated column. By-products such as water and dimethyl ether areobtained together with the methanol. In the distillation, the energy ispreferably introduced via the bottom of the column, for example by meansof a bottom circuit. The temperature at the bottom should be at least100° C. It is advantageous to keep the temperature of the feed to thecolumn above 20° C., for example at the level at which the hydrogenationproduct mixtures are obtained so that their thermal energy can beutilized in the column. The average residence time of the 1,6-hexanedioltogether with the abovementioned high boilers and higher-boiling estersat temperatures of at least 100° C. in this column is at least 5minutes. This 1,6-hexanediol-comprising stream is advantageouslyprocessed in a further column to give 1,6-hexanediol having a proportionby weight of nitrogen of less than 5 ppm. Here, it is possible to use,for example, a dividing wall column or a column having a side offtake inwhich the low boilers such as 1-hexanol, 1-methoxy-6-hydroxyhexanetogether with very little 1,6-hexanediol are distilled off at the top,high boilers and/or higher-boiling esters which likewise comprise verylittle 1,6-hexanediol are taken off at the bottom and liquid or gaseous1,6-hexanediol having a nitrogen content of less than 5 ppm is taken offvia the side offtake. This 1,6-hexanediol preferably comprises less than3 ppm of nitrogen. This column is operated at a temperature at thebottom of above 100° C. and average residence times of more than 5minutes. The nitrogen-comprising components are discharged to an extentof at least 50% with the high-boiling bottom stream.

Instead of the one column having a side offtake, it is also possible touse two separate columns, with low boilers being removed at the top inthe first column and the 1,6-hexanediol then being distilled off fromhigh boilers and/or higher-boiling esters in the second column. Atemperature of at least 100° C. with average residence times of at least5 minutes is set at the bottom of at least the first of the two columns.

To prepare relatively small amounts of 1,6-hexanediol, use can also bemade of batch columns in which the hexanediol is purified batchwise.Here, low boilers compared to hexanediol are separated off first,followed by the 1,6-hexanediol itself. High boilers and higher-boilingesters comprising the nitrogen components remain in the bottom.

A further variant is to add carboxyl-comprising components other thancarboxylic acids and esters after the hydrogenation. These compoundsare, for example, aldehydes and ketones which with the 1,6-hexanediolform compounds which have boiling points higher than that of1,6-hexanediol itself.

If water is used as solvent, it is useful to hydrogenate the adipic aciditself. As hydrogenation catalyst, it is then possible to use, forexample, Co- , Re- and Ru-comprising catalysts. Here too, the conversionof carboxylic acids and/or esters should be incomplete, so that theproportion of carboxylic acids and/or esters in the hydrogenationproduct mixture is preferably above 500 ppm, particularly preferablyabove 1000 ppm.

The 1,6-hexanediol prepared in this way, which has a nitrogen (N)content of less than 5 ppm, can be used in any process for preparingpolymers in which diols are used. Since the 1,6-hexanediol has an Ncontent of less than 5 ppm, polymers can be obtained therefrom withoutproblems. The 1,6-hexanediol obtained according to the invention ispreferably used for the preparation of polyurethanes and polyesters.Here, the 1,6-hexanediol is reacted with diisocyanates such ashexamethylene diisocyanate, tolylene 2,4-diisocyanate, diphenylmethanediisocyanate, isophorone diisocyanate and4,4′-diisocyanatodicyclohexylmethane to form polyurethanes. To preparepolyesters, the 1,6-hexanediol obtained according to the invention isused in the presence of dicarboxylic acids such as succinic acid, maleicacid, fumaric acid, glutaric acid, adipic acid, dodecanedioic acid,terephthalic acid, isophthalic acid and phthalic acid.

EXAMPLES Example 1

Adipic acid, obtainable as product of the oxidation ofcyclohexanol/cyclohexanone by means of nitric acid, having a content of4 ppm of nitrogen is esterified by means of an acidic ion exchanger ascatalyst (Amberlite IR 120) and methanol to form dimethyl adipate. Aftercomplete esterification and removal of the ion exchanger and excessmethanol, the ester is distilled (18 mbar, boiling point: 115° C.) andobtained in a purity of 99.98%. The nitrogen (N) content of the esterwas 4 ppm. The dimethyl adipate is hydrogenated in the gas phase at 60bar and 195-210° C. over a copper-comprising catalyst. The spacevelocity over the catalyst is 0.15 kg of ester feed/liter of catalystper hour. The reactor is a shaft reactor preceded by a vaporizer inwhich the feed stream is vaporized at about 195° C. with the aid of astream of hydrogen gas. The stream of hydrogen gas is composed of freshgas (4.5 mol/mol of dimethyl adipate) and a recycle gas stream (about 80mol of hydrogen/mol of feed stream). Downstream of the reactor, thegaseous mixture is cooled and liquid products are taken off. The gaseousoutput is recirculated by means of a recycle gas compressor. A smallpart of the gas stream is discharged as offgas. The dimethyl adipateconversion is about 99.9%. A little methanol was lost via the offgasstream. The collected outputs (about 30% by weight of methanol, about68% by weight of 1,6-hexanediol, about 0.5% by weight of methyl6-hydroxycaproate and 0.06% by weight of hexanediol ester of6-hydroxycaproic acid, about 0.3% by weight of hexanol, 0.1% by weightof dimethyl adipate, balance in each case below 0.1% by weight) have anN content of 5 ppm and are worked up by distillation. Here,predominantly methanol is removed at temperatures at the bottom of up to140° C. and pressures of from 1013 mbar absolute to 100 mbar over aperiod of one hour. The remaining bottoms (about 0.08% by weight of1,6-hexanediol methyl adipate, 0.02% by weight of the di-1,6-hexanediolester of adipic acid, 0.3% by weight of the 1,6-hexanediol ester of6-hydroxycaproic acid) is fractionally distilled batchwise in adistillation column (1 m packed column, reflux ratio 5, no entry of air)at 100 mbar absolute and temperatures at the bottom of about 185° C.over a period of two hours. After removal of low boilers such asresidual methanol and hexanol, 1,6-hexanediol is obtained in adistillation yield of about 90% with a purity of 99.9% and an N contentof 1 ppm. The N content in the remaining bottom is 15 ppm.

Comparative Example 1

Example 1 is repeated with the difference that a second reactor whichcorresponds in terms of dimensions and capacity to the first and throughwhich the reaction mixture flows after the first reactor is additionallyinstalled in the hydrogenation. Accordingly, the space velocity over thecatalyst decreases to 0.75. The conversion of dimethyl adipate wasvirtually quantitative, and the output comprised methanol and hexanedioltogether with 6-hydroxycaproic esters in the form of methyl andhexanediol esters in amounts of less than 0.03% by weight, about 0.6% byweight of hexanol, a balance in each case less than 0.05% by weight. Theoutput again has an N content of 5 ppm. It is worked up further to give1,6-hexanediol as in example 1. The resulting 1,6-hexanediol had an Ncontent of 5 ppm, and the bottom product had an N content of 7 ppm.

1. A 1,6-hexanediol having a proportion by weight of nitrogen of lessthan 5 ppm and obtained by a process comprising: I) distillation of amixture comprising 1,6-hexanediol and more than 500 ppm of at least onecarboxylic acid, ester, or both, having a boiling point higher than thatof the 1,6-hexanediol and being in contact with the 1,6-hexanediol at atemperature range greater than or equal to 100° C. for at least 5minutes before, during, or before and during, the distillation; and II)collection of the 1,6-hexanediol having a nitrogen content of less than5 ppm.
 2. The 1,6-hexanediol of claim 1, wherein the distillation iscarried out in the absence of oxygen.
 3. The 1,6-hexanediol of claim 1,wherein the at least one carboxylic acid, ester, or both, is added tothe mixture before the distillation.
 4. The 1,6-hexanediol of claim 3,wherein the distillation is carried out in the absence of oxygen.
 5. The1,6-hexanediol of claim 1, wherein the mixture comprises at least oneester.
 6. The 1,6-hexanediol of claim 2, wherein the mixture comprisesat least one ester.
 7. The 1,6-hexanediol of claim 3, wherein themixture comprises at least one ester.
 8. The 1,6-hexanediol of claim 1,wherein the distillation is carried out in a range from 10 to 3000 mbar.9. The 1,6-hexanediol of claim 1, wherein the distillation is carriedout batchwise.
 10. The 1,6-hexanediol of claim 1, wherein thedistillation is carried out continuously.
 11. The 1,6-hexanediol ofclaim 1, wherein the 1,6-hexanediol has a proportion by weight ofnitrogen of less than 3 ppm.
 12. The 1,6-hexanediol of claim 1, whereinthe 1,6-hexanediol has a proportion by weight of nitrogen of less than 2ppm.
 13. The 1,6-hexanediol of claim 1, wherein: a) the distillationemploys at least one dividing wall; b) the distillation employs a columnhaving at least one side offtake, wherein at least one low-boilingcompound is distilled off at the top of the column, at least onehigh-boiling compound is taken off at the bottom of the column, andliquid or gaseous 1,6-hexanediol is taken off at the at least one sideofftake; or c) the distillation employs at least two separate columns,wherein at least one low-boiling compound is removed at the top of afirst column, and the 1,6-hexanediol is distilled off in a secondcolumn.
 14. A polymer obtained by reacting the 1,6-hexanediol of claim 1with at least one reactive compound.
 15. The polymer of claim 14,wherein the at least one reactive compound comprises a diisocyanate. 16.The polymer of claim 15, wherein the at least one reactive compoundcomprises at least one selected from the group consisting ofhexamethylene diisocyanate, tolylene 2,4-diisocyanate, diphenylmethanediisocyanate, isophorone diisocyanate and4,4′-diisocyanatodicyclohexylmethane.
 17. The polymer of claim 14,wherein the at least one reactive compound comprises a dicarboxylicacid.
 18. The polymer of claim 17, wherein the at least one reactivecompound is at least one reactive compound comprises at least oneselected from the group consisting of succinic acid, maleic acid,fumaric acid, glutaric acid, adipic acid, dodecanedioic acid,terephthalic acid, isophthalic acid and phthalic acid.
 19. The polymerof claim 14, wherein the 1,6-hexanediol has a proportion by weight ofnitrogen of less than 3 ppm.
 20. The polymer of claim 14, wherein the1,6-hexanediol has a proportion by weight of nitrogen of less than 2ppm.